What must be specified when not included in the Standard Instrument Departure (SID)?

When a Standard Instrument Departure (SID) does not include a specific altitude, it is important to specify the altitude that the aircraft is expected to maintain during the initial phase of its departure. This specification ensures that the aircraft climbs safely and remains within controlled airspace, preventing potential conflicts with other air traffic. Altitudes are critical for maintaining safe vertical separation between aircraft and for managing the overall flow of air traffic, especially in busy terminal areas.

In the case where a SID does provide an altitude, pilots are expected to follow it; however, when it's absent, the onus falls on the pilot or flight planner to establish what the initial climbing altitude should be, in compliance with air traffic control regulations and safety standards. This helps maintain an orderly departure and ensures that all operating parameters are clearly understood by both pilots and air traffic control.